The Denver-based chain known for its hefty burritos is pledging to use a set amount of local produce at each of its more than 730 restaurants around the country -- when produce is in season.

This summer, Chipotle is purchasing 25 percent of at least one produce item for each of its stores from small and mid-sized farms located within about 200 miles. Those purchases could include lettuce, onions and peppers.

Organic beans, avocados and herbs grown only on a large scale in certain climates won't be part of the program.

Fine dining chefs have long sought ingredients from nearby farmers, but Chipotle is moving that philosophy to a growing quick-service chain.

"It's going to open up the practice of knowing where food comes from to a wider variety of people," said Kate Evanishyn of Slow Food USA, which believes in food production that treats the environment, animals, human health and workers well.

"Ultimately this is changing the way the world thinks about and eats fast food," Chief Executive Steve Ells, who founded the company, said.

Ells, a graduate of the Culinary Institute of America, said it's about getting the best tasting food. The program marks an extension of the "Food With Integrity" slogan for the chain, which only serves naturally raised pork and chicken.

Ingredients taste fresher when they don't travel as far to get to the table, and they taste better when raised without chemicals, Ells said. Using local food means using less fuel to transport ingredients, and it supports the local economy, he said.

Ann Daniels, executive director of purchasing, said using more local ingredients will lower expenses in some cases and raise them in others, but food costs won't significantly change either way. She said the policy will stay in place even as Chipotle adds stores.

Finding the right suppliers, though, has been a challenge. During a test last year, Chipotle discovered it would have to use mid-size farms of about 500 to 600 acres to ensure a reliable supply. Tiny growers were less able to survive swings in weather or couldn't always deliver a product, Daniels said.

The company turned to distributors, local employees and the Web to find producers and then checked that each met its standards, such as those for food safety.

Daniels said Chipotle has 30 to 50 farms on its list so far.

Among them is third-generation farmer Kirk Holthouse of Holthouse Farms in Willard, Ohio. His family's 500-acre farm will provide jalapeno peppers, romaine lettuce and green bell peppers to Chipotle in Ohio, Pennsylvania, Indiana, Kentucky and Michigan.

He said he was glad to hear a chain was interested in local produce.

"In the summertime, quite often, we don't get some of that business because a lot of chain restaurants will be buying out of California," from farms 10 to 20 times larger, Holthouse said.

His farm usually ships about 1,000 truckloads a year. Chipotle's orders could add an extra truckload a week, he said.

Chipotle's initiative comes amid a weak economy, with diners eating out less. In a note to investors this week, Deutsche Bank analyst Jason West said the chain's same-store sales, or sales at locations open at least a year, have decelerated in each of the last four quarters.

Chipotle has not commented on West's note, but Ells said last week that the chain is committed to adding more local ingredients and suppliers and to include smaller farms.